The subject matter disclosed herein relates to a liquefaction system. Specifically, the present disclosure relates to systems and methods for generating liquefied natural gas using one or more turboexpanders.
Natural gas, when isolated from natural sources (e.g., underground in naturally occurring reservoirs), generally includes a mixture of hydrocarbons. The major constituent in these hydrocarbons is methane, which is generally referred to as natural gas in commerce. Natural gas is useful as a source of energy because, among other things, it is highly combustible. One particularly desirable characteristic of natural gas is that it is generally considered to be one of the cleanest hydrocarbons for combustion. Because of this, natural gas is often used as fuel in a wide variety of settings, including heaters in residential homes, gas stoves and ovens, dryers, water heaters, incinerators, glass melting systems, food processing plants, industrial boilers, electrical generators among numerous others. Generally, natural gas (e.g., untreated or raw natural gas) removed from reservoirs is processed and cleaned prior to entering pipelines that eventually feed the gas to homes and industrial plants. For example, natural gas may be processed to remove oil and condensates, water, sulfur, and carbon dioxide. During these processes, natural gas may be liquefied, which may facilitate separation (e.g., purification) and transport.
Natural gas may be transferred to various destinations via pipelines or, in certain situations, via storage vessels. Unfortunately, pipeline networks can represent a significant investment, and are generally used only in situations where the natural gas is traveling a relatively short distance. When natural gas is extracted far from its final destination, transportation by way of storage vessels may be more economical. Indeed, as oil and coal resources become scarcer, the demand for liquefied natural gas has increased because of its ability to be transported to destinations that do not have access to a pipeline.
In these situations, the natural gas may be liquefied, transported in a vessel that will keep the gas at cryogenic temperatures, and re-vaporized upon arrival at its destination. Natural gas condenses to its liquid state at atmospheric pressure at about −260° F., or approximately −162° C. Accordingly, it should be appreciated that reaching such a low temperature on a large scale, while also maintaining these temperatures during transport, can be challenging. For example, traditional refrigeration techniques may be sufficient to reach or maintain these temperatures. However, these techniques can often involve significant capital investment, such as in refrigerant, compressors, and so forth. Therefore, typical approaches to liquefying natural gas may be subject to further improvement.